Radio position indicating system



,'sgept. 9, 1947,

A l D. G. .C. LUCK.

RADIO POSITION INDICATING SYSTEM hFiled Nov. 14, 1942 qf/mera 5 Sheets-Sheet 1 SePt- 9, 1947- D. G. c. LUCK 2,427,220

RADIO POSITION INDICATING SYSTEM Filed Nov. 14, 1942 3 sheets-sheet 2 a Pl-E 7 Il-?l Z Q'vfmo Snventr Y DQ'WDIGLLUCH f sept.9,1947. AD. G1 c. LUCK 2,427,220

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IN V EN TOR.

A ORNE Y Patented Sept. 9, 1947 UNHTED RADO PSTEON INDCATING SYSTEM David G. C. Luck, Hightstown, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application November 14, 1942, Serial No. 465,525

7 Claims. l

The invention relates to radio position finding, and more particularly to systems for indicating the position of a mobile craft with respect to a plurality of nxed stations, using relayed transmissions between the fixed stations and the mobile station. The distance from the mobile station of each of the iixed stations is determined by the time required for a signal to travel from the mobile station to the fixed station, and back to the mobile station. The position of the mobile station may be determined on a map by plotting circles centered at the positions of the fixed stations with radii corresponding to the respective distances.

It is the principal object of the present invention to provide an improved indicator means for such systems. Another object is to provide an improved method of and means for automatically plotting the position of a mobile station upon a map or chart placed over the screen of a cathode ray tube. These and other objects will become apparent to those skilled in the art upon consideration of the following description, with reference to the accompanying drawing of which Fig. 1 is a schematic block diagram of one embodiment of the invention, Fig. 2 is a modification of Fig. 1, Fig. 3 is a group of graphical representations of voltages in the operation of the system of Fig. 2, Fig. 4 is a circuit diagram of the electronic switch indicated in Fig. 2, and Figure 5 is a further modification of Figure 1.

. Referring to Fig. 1, the system comprises a mobile station including a pulse transmitter i, and pulse receivers 3 and 5. A pulse generator 1 is connected to the transmitter I and to a sawtooth voltage generator 9. A sweep voltage generator II is connected to a modulator I3 which is arranged to be controlled by the output of the sawtooth generator 9. The output circuit of the modulator I3 is connected through a switch I and adjustable bias control circuits I1 and I9 to the vertical deection circuits of a double gun cathode ray tube 2|. The switch I5 is also connected through a 90 phase shifter 23 and adjustable bias control circuits and 21 to the horizontal deection circuits of the tube 2i. The pulse receiver 3 is connected through a switch 29 to an intensity control electrode SI of the tube The pulse receiver 5 is similarly connected to the other intensity control electrode 33. The switch 29 is arranged to disconnect the electrodes 3'I and 33 from the receivers 3 and 5, and connect them to a direct current source 35. The switches I5 and 29 arelmechanically ganged, as indicated 4by the dash line 31.

Ground stations 39 and I are provided at fixed reference locations. Each ground station comprises a receiver tuned to respond to signals from the pulse transmitter, and a transmitter, operating at a frequency different from that of the transmitter I connected to the output of the receiver. The pulse receiver 3 is tuned to respond to signals from the transmitter of the ground station 39 and the pulse receiver 5 is tuned to respond to signals from the transmitter of the ground station lil, which operates at a frequency diiierent from those of the pulse transmitter I and the transmitter of the' ground stanon 39. l'

The adjustment and operation of this system is as follows:

'Ihe switch I5 is opened and the switch 29 is operated to connect the source 35 to the control electrodes 33 and 3I. The bias control circuits I1, I 9, 25 and 21 are manually adjusted to set the undeiiected spots of the cathode ray guns at points 43 and 45 on the screen, corresponding to the mappositions of the ground stations 39 and @l respectively. The switch I5 is then closed and the switch 29 moved to connect the receivers 3 and 5 to the electrodes 31 and 33. The output voltage of the sweep generator l I passes through the modulator I3 and is split into two phases by means of the phase shifter 23, producing circular scanning of the two cathode ray beams about the centers 43 and 45. The amplitudes of the scanning voltages and hence the radius of the arcuate scanning patterns is controlled by the modulator I3. The sawtooth generator 9 is synchronized with the pulse generator 1 and controls the modulator VI3 providing cyclical sawtooth variations of the amplitude of the deiiection voltages applied to the tube 2|. With each pulse from the generator 1, the radius of the scanning pattern starts at zero and increases uniformly throughout the pulse period. The electrodes 3l and 33 are normally biased to cut off the cathode ray beams, so that no visible traces are produced on the screen.

Each pulse from the generator 1 is transmitted to the ground stations 39 and 4I which respond by retransmitting a similar pulse to the receivers 3 and 5 respectively. The receiver output circuits are so poled as to oppose the bias on the electrodes 3l and 33. Thus the radial scanning cycle is initiated simultaneously with each transmitted pulse; each received pulse momentarily overcomes the beam cutoi bias at the instant of receptionof the return pulse, producing an illuminated trace at a radius corresponding'to'the distance of the respective ground station from the mobile station. The pulse generator provides a train of pulses cyclically repeating at such a rate that traces present the appearance of steady illumination. The trace 41, centered about the point 43, is applied to the screen by the momentary biasing eiect of the return signal from the ground station 39. The trace 46. is similarly applied to the screen by the effect of the signal from the ground station 4|. These traces .intersect at two points, 5| and 5.3, one of which corresponds to the map position of the mobile station, and the other of which is ambiguous. Usually the operator will have enough additional information, such as his approximate position, or the bearing of one of the ground stations, 'to enable him to select the correct one of the two intersections. However, if an unambiguous indication is required, a third ground station 4B and a third mobile receiver 4 may be used, with an additional ycontrol channel i8, 26 and a three gun cathode ray tube,2| as illustrated by Fig. 5. A third trace 48 will be produced,- intersecting traces 45 and `4,1 at the point 53.

Fig. 2 shows a modi-cation of Fig. 1. In this arrangement the circular scanning pattern is swept inwardly from the maximum radius to that corresponding to the distance. radius is maintained for the remainder of the pulse repetition period, producing a luminous trace as a result of the repeated sCf2.I11f.-u`ngr at that. radius. Referring to Fig. 3, the receivedpulse initiates the radial scanning cycle and the next transmitted pulse stops the radial scanning; the radius is maintained constant until the following return pulse is received. No intensityr control of the beam is required, since the inward motion of the scanning pattern is too. rapid to. produce a visible trace. This arrangement has the advantage of producing a more brilliant indication than the system of Fig. 1. A furtheradvantagalies in the fact that the trace is of approximately uniform intensity, independent of the radius. This is because the scanning is. maintained,y for a longer portion of the pulse period at` the greater radii, thus compensating thehigher spot velocity.

This system includes a sweep voltage; gnerator l, pulse generator 1, pulse transmitter I., ground stations 39, and 4l, and pulse receivers 3. and. 5, similar to the correspondingly designated elements of Fig. l. A pair of electronic `switches 4 and 4 are connected. to the sweep Voltage gen.- erator li,l pulse generator 1. and to theA receivers 3 and 5 respectively. The circuits 4, and'4. are connected to modulators. |,3. and |23?. rIhe sweep generator is connected.throughthemodulators to phase splitters, 24. and 2 4', and. thence through centering controls 2B and 26 to the deflection. clements 20 and 2 0 respectively of the tube 2|. The phase splitters andA centering. controls are similar to the corresponding elements4 illustrated in Fig. 1.

Referring to Fig. 4, the electronic switch 4. in,- cludes a pair of vacuum tubes Ill!)4 and ||I|' connected as direct current amplifiers, with the input of each connected tothe output of the other. The plate circuit of the tube is connected through a resistorV 3- and" a diode-'rectier ||i4 to a capacitor H5. The time. constant of this R-C circuit is maderela-tively long withrespect to the pulse repetition period of the generator 1. A gaseous dischargetube ||1 is connected across the capacitor H45, whichis also connectedto the control input circuit ot the-modulator |3; The control grid of the tube |"|;1y is connected to the 4 pulse receiver 3 and the control grid of the tube |09 is connected to the cathode of the tube |l1. A resistor I9 is included in the cathode circuit of the tube ||1.

The operation of this system is as follows:

Each pulse produced by the generator 1 is transmitted to the echo or ground station, then relayed to the receiver 3. When the return pulse appears at the receiver 3, the tube |1 is fired, short circuiting the capacitor H5. This reduces the bias on the modulator I3 to its minimum value, producing the maximum amplitude of sweep voltage output. The discharge current of the capacitor H5 produces a voltage drop across the resistor H9, overcoming the cutoii bias on the grid of the tube |59, and cutting oir the tube The voltage of the` plate of the tube goes` positive, initiating constant-current charging of the capacitor H5. This continues for the remainder of the pulse repetition period, decreasing the output of the modulator i3 until the next pulse. is generated by the generato-r 1. This pulse. overcomes the cui-.01T bias on the tube and cuts olf the tube |89. The voltage at the plate of the tube goes to its minimum value, and charging of the capacitor |.|5 stops. Since the tube ||1. is non-conductive at this time and the rectifier ||4 prevents discharge through the resistor |.|.3, the voltage on` the capacitor |j|j5 remains. substantially constant until the next received pulse fires the tube ||1. During this. interval the sweep voltage output of the modulator |3 remains constant at an amplitude corresponding to the. phase difference betweenthe transmitted pulse andthe received pulse. The above cycle or Operation is repeated with each pulse from receiver 3', producing a succession of' superimposed traces at such a rate as to present the appearance of constant illumination.

The second channel of4 the system comprises the electronic switch 4f" which is a duplicate of the electronic switch modulator I3", phasesplitter 2li' and centering control' 26"', andr operates in the same manner as. the above described channel. The resulting tracesypresent the same appearance and are interpreted in the same manner* as those produced by the system of Fig. 1.

Thus the invent-ion has been described'as` an improved position indicator system fortravel' time distance measuring systems. Circular traces-,are produced on the face of a cathode ray' tube',v centeredV at positions; corresponding to the known Vlocations of ground stations; an'dautomaticallycontrolled so that their radii correspond to the dis.- tances of the respective ground stations from a mobile-station. One point ofY intersection of.' the circular rtraces then corresponds tothe position of; the mobile station.

I claim asl my invention:

l. A radio position indicating system including means arranged to provide a reference pulse train and plurality of Asynchronous. trains of pulses, each delayed with respect t0. said reference pulse train byv an interval proportional to a respective distance to be plotted, acathode ray tube. means for providing a pluralityof' circular scanning patterns on saidtube, adjustable -bias meansarranged to center each of saidf scanning patterns, about a predetermined point, means for. cyclicallyvaryingV the radius; ofi' said; scanning patterns responsefto-said reference train4 and' means forcycli'.- cally varyingv the intensityof illumination of'each of said-patternsinresponse to; a respective one of saidV delayed pulsetrains.

2. The method of plottingY the' position of a mobile station with respect to the position of a plurality of fixed stations, on the face of a cathode ray tube, comprising the steps of producing a train of reference pulses, deriving a plurality of synchronous trains of pulses delayed with respect to said reference train by intervals proportional to the respective distances of said fixed stations from said mobile station, producing a plurality of substantially circular cathode ray scanning patterns centered about points corresponding to the respective positions of said xed stations, cyclically varying the radii of said scanning patterns in response to said reference train, and cyclically varying the intensity of illumination of said scanning patterns in response to respective ones of said delayed trains.

3. The method of plotting on the screen of a cathode ray tube a position in terms of its distances from a plurality of pre-determined reference points, comprising the steps of producing a reference wave train, deriving a plurality of synchronous wave trains, each delayed with respect to said reference train by an amount proportional to one of said distances, producing a plurality of substantially circular cathode ray scanning patterns centered at positions corresponding resepctively to the positions of said reference points, cylically varying the radii of said scanning patterns in response to said reference waves, and cyclically varying the intensity of each of said scanning patterns in response to a respective one of said delayed waves.

4. A radio position indicating system including a mobile station, an impulse generator at said mobile station, means for transmitting signals from said mobile station in response to the output of said impulse generator, a plurality of xed stations comprising means responsive to signals from said mobile station to transmit signals to said mobile station, cathode ray indicator means at said mobile station, deection voltage generator means arranged to provide substantially circular scanning patterns on said cathode ray means, adjustable bias means for centering each of said circular patterns about a predetermined point, modulator means arranged to vary said deection voltages cyclically in response to said impulse generator, and. means for varying the intensity of illumination of each of said scanning patterns in response to the signal received at said mobile station from a corresponding one of said xed stations.

5. A radio position indicating system comprising a mobile station including means for transmitting signals, xed stations each including means responsive to said transmitted signals to transmit similar signals to said mobile station to produce at said mobile station a plurality of signals similar to signals transmitted by said mobile station but delayed with respect thereto by intervals proportional respectively to the distances of said fixed stations from said mobile station, a pulse generator arranged to control the transmissions from said mobile station, a sawtooth wave generator controlled by said pulse generator, a cathode ray tube, deflection voltage generator means arranged to produce a plurality of circular scanning patterns on the screen of said cathode ray tube, modulator means arranged to control the amplitude of said deflection voltages in response to said sawtooth wave generator, adjustable bias means arranged to control the positions of said scanning patterns, and means for controlling the intensity of illumination of each of said scanning patterns in response to a corresponding one of said delayed signals.

6. A radio position indicating system including means arranged to provide a reference pulse train and a plurality of synchronized pulse trains, each delayed with respect to said reference puls train by an interval proportional to a respective distance to rbc plotted, a cathode ray tube, means for providing a plurality of circular scanning patterns on said tube, adjustable bias means arranged to center each of said scanning patterns about a predetermined point, means for cyclically varying the radius of each of said scanning patterns in response to said reference train, and means for stopping the variation in radius of each of said patterns during each cycle of said reference train for a period related in magnitude to the delay of a corresponding one of said delayed trains.

7. A radio position indicator system comprising a control station and a plurality of reference stations, said control station including a pulse generator, a pulse transmitter connected to said pulse generator and arranged to transmit signals to saidreference stations, a receiver and a transmitter arranged to be modulated by the output of said receiver at each of said reference stations, a plurality of receivers at said control station each arranged to respond to the signal from one of said reference stations, a cathode ray tube including a plurality of deection voltage input circuits, a deflection voltage generator, modulator means connected to said deection voltage generator, phase splitting circuits connected between said modulator means and said deflection input circuits to provide a plurality of circular scanning patterns on said cathode ray tube, a sawtooth wave generator, an electronic switch means connected to said pulse receivers and to said sawtooth generator and arranged to control said modulator means whereby the radius of each of said scanning patterns is cyclically varied between an upper limit and a value proportional to the distance of a corresponding one of said reference stations from said control station.

DAVID G. C. LUCK.

REFERENCES CITED The following references are of record in the iile of this patent:

UNITED STATES PATENTS Number Name Date 1,750,668 Green Mar. 18, 1930 2,301,929 Budenbom Nov. 17, 1942 2,134,716 Gunn Nov. 1, 1938 2,209,191 Dearing July 23, 1940 2,183,634 Zworykin 1 Dec. 19, 1939 FOREIGN PATENTS Number Country Date 406,903 Great Britain Mar. 8, 1934, 

